The present invention relates generally to oil seals, and more particularly, to seals with associated wear sleeves and on which the wear sleeves possess a hydrodynamic pattern. In connection with the oil seal itself, the grooves or formations on wear sleeve work to pump slightly leaking oil from the xe2x80x9cairxe2x80x9d side under the seal to the xe2x80x9coilxe2x80x9d side of the seal.
With automobile and truck manufacturers being forced by general improvements in the products and by competition to extend longer and longer warranties, the oil seal remains a problem of concern to the auto industry. Not only must the seal be responsible for its own performance, but owing to the inaccessible location of most oil seals, the labor involved in replacing worn out or faulty seals is many times in excess of the cost attributable to the oil seal itself. As the result of this consideration, among others, there has been an increasing emphasis on the use of PTFE (polytetrafluoroethylene) or like materials as the primary lip in oil seals. In particular, many very high-mileage applications such as trucks and tractors used with semi-trailers, pose particular problems.
The PTFE or xe2x80x9cTeflonxe2x80x9d type materials are commonly filled with graphite, fiberglass, and other components known to those skilled in the art. However, in an attempt to manufacture oil seals which are hydrodynamic in character and which also include xe2x80x9cTeflonxe2x80x9d components, there have arisen several problems, particularly with hydrodynamic seals. The resinous xe2x80x9cTeflonxe2x80x9d lips contain hydrodynamic formations which tend to wear long before the seals.
The first approach which was tried to alleviate this problem was to impress a hydrodynamic pattern on the shaft or the like. However, this created several problems of expense which really cannot readily be overcome. Hence, the idea of grooving or notching a shaft involves complex machine operations which must be performed xe2x80x9cin the roundxe2x80x9d, that is, impressed on the shaft after the same is manufactured. Besides machining, this also calls for heat treating or other surface treating, also xe2x80x9cin the round.xe2x80x9d
Now, because of the desire of automotive and other manufacturers to look to only one supplier as a source for oil seals, it is common for a seal which is sold for a certain application also to include the parts required to make the complete seal, i.e., one supplier now makes both wearing surfaces. Hence, the ordinary seal of this type includes what is known as a wear sleeve as well as the seal itself. The seal is normally made from rubber, but in many cases is made from Teflon or the like, or at least includes a Teflon wear surface.
At least one proposal has been made to form the hydrodynamic pattern on the axial flange of the wear sleeve. Accordingly, in Horve Patent No. 5,350,181, a portion of the sleeve was shown as being drawn and at the same time, being forced into an embossed pattern on the drawing die. As a consequence, as shown in that patent, a pattern of angled ribs could be formed on the wear sleeve. However, this process involved many of the same problems in respect to the die as would otherwise occur with the shaft, namely, cutting or forming hydrodynamic ribs in the die, which ribs would then require hardening so the die could be used many times.
Thus, impressing a hydrodynamic pattern in the die over which the axial flange of the wear sleeve was formed involved a somewhat laborious case of cutting all but the ribs into the die or otherwise forming the pattern on the drawing die. Such a pattern was required to be formed in the ring which was then used in the drawing process. Accordingly, the die required surface hardening thereafter. Such a process was, particularly for flanges of varying sizes, unduly expensive. However, such a seal held out the promise of placing the hydrodynamic pattern on the metal wear sleeve rather than on the PTFE lip, and in this sense was considered advantageous if somewhat impractical.
Hence, it would be advantageous to provide an improved form of hydrodynamic seal, particularly one that is effective with PTFE or the like seals.
It is an object of the present invention is to provide a two-piece seal having a seal member and a wear sleeve member, with the wear sleeve including a formation, preferably a bidirectional pattern, that is coined or stamped therein, and made by a novel process.
Another object of the present invention is to perform a stamping or coining operation on the wear sleeve blank and thereafter, forming the wear sleeve to its finished dimension.
Yet another object of the invention is to provide a wear sleeve having a stamped or coined pattern therein consisting of several circular grooves, whose center is slightly offset with respect to the center of the wear sleeve blank, whereby, when the wear sleeve is drawn so as to include an axial flange, the depressions or the like form a bidirectional pumping pattern in the wear sleeve.
Still another object of the invention is to provide such a wear sleeve with a stamped or coined portion therein, which is subsequently elongated into an axial flange, all without loss of effectiveness.
In this method, a much more economical and satisfactory way of creating a wear sleeve that has a hydrodynamic pattern impressed therein has been discovered.
In this method, a simple series of concentric circular grooves, slightly offset to create a pumping pattern, are formed in the wear sleeve blank of the seal assembly while the wear sleeve blank is in a flat condition. Thereafter, the flat blank used in forming the wear sleeve is drawn so that, in addition to the ordinary installing curl, an axial flange is formed in the wear sleeve which carries the same hydrodynamic pattern that was stamped or coined in the wear sleeve blank while it was in a flat condition. The method of making the wear sleeve thus includes merely stamping or coining a grooved pattern in the flat sleeve, whereupon the sleeve may be drawn and the axial flange thereof will undergo a somewhat reduced thickness and elongated form.
Thus, although the length of the axial flange may be somewhat elongated, as for example up to 30% longer than the original portion selected for drawing, the depth and configuration of the grooves which afford the hydrodynamic action are relatively unchanged. In some cases, where the depth of the groove is reduced significantly, it may be accommodated merely by stamping or coining the pattern to a greater depth in the blank before the blank is drawn.
Accordingly, it is possible to manufacture an oil seal having the advantages of an axial wear sleeve hydrodynamic pattern including a bidirectional pattern, without the expense and difficulty formerly thought necessary to create such a product.
The manner in which these and other objects of the present invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the invention and shown in the accompanying drawings wherein like reference numbers indicate corresponding parts throughout.